1. Technical Field
This document relates to an air conditioner. For example, this document relates to an air conditioner and the control method thereof capable of reducing noise.
2. Discussion of the Related Art
In general, an air conditioner is an apparatus for cooling and/or heating an indoor space by the processes of compressing, condensing, expanding and evaporating refrigerant.
The air conditioner comprises an outdoor unit and an indoor unit connected to the outdoor unit. Air conditioners are classified into a general type air conditioner having one indoor unit connected to one outdoor unit, and a multi-type air conditioner having a multitude of indoor units connected to one outdoor unit.
Alternatively, air conditioners are classified into a cooling system supplying only cool air into the indoor space by operating the refrigerant cycle only in one way, and a cooling and heating system supplying cool or warm air into the indoor space by operating the refrigerant cycle in both ways optionally.
An air conditioner is basically forming a refrigerating cycle including a compressor, an outdoor heat exchanger, an expansion valve and an indoor heat exchanger.
The gaseous refrigerant compressed at the compressor is turned into liquid after flowing into the outdoor heat exchanger. The refrigerant radiates heat to outside as it is turned into liquid at the outdoor heat exchanger. After that, the refrigerant discharged from the outdoor heat exchanger is expanded when passing through the expansion valve and is flowed into the indoor heat exchanger.
The liquid refrigerant flowed into the indoor heat exchanger is turned into gaseous refrigerant. The refrigerant absorbs the outer heat as being phase-changed at the indoor heat exchanger.
The air conditioner generally has a cooling/heating operation mode to cool and heat the indoor space, a defrost operation mode to remove frost generated by the cooling/heating operation of the air conditioner, and an oil recovery operation mode to recover oil flowing with the refrigerant.
The opening degree of the expansion valve is predetermined to a fixed value for the cooling/heating mode, the oil-recovery operation mode, and the defrost operation mode. That is, the expansion valve of the conventional air conditioner maintains a predetermined opening degree regardless of the operation modes of the air conditioner.
As the blowing noise and operation noise generated during the cooling/heating mode of the air conditioner are familiar to human ears, the users don't react to the noises sensitively.
On the other hand, the refrigerant flowing noise generated during the oil recovery operation mode and defrost operation mode of the air conditioner has frequencies harsh to human ears. Especially, the flowing noise due to the flowing of the refrigerant is increased at the spot passing through the expansion valve.
The graph illustrated in FIG. 1 indicates the noise generated during the oil recovery operation mode and defrost operation mode of an air conditioner.
There are two peak values P10, P20 for the flowing noise generated at the early stage of the operation during the oil recovery operation mode and the defrost operation mode. The frequencies at the peak values are the frequencies harsh to human ears, and thus the noise is heard sensitively to the users.
The noise due to the flowing of the refrigerant has become the main complaint from consumers, and it has caused the deterioration of the reliability of the product.
It is possible to install a noise-reducing device such as a muffler or a strainer at around the expansion valve to reduce the flowing noise. However, such additional installation of the noise-reducing device increases the installing cost of the air conditioner.